generatePassword.php

<?php
function generatePassword($l = 8, $c = 0, $n = 0, $s = 0) {
    // get count of all required minimum special chars
    $count = $c + $n + $s;

    // sanitize inputs; should be self-explanatory
    if(!is_int($l) || !is_int($c) || !is_int($n) || !is_int($s)) {
        trigger_error('Argument(s) not an integer', E_USER_WARNING);
        return false;
    }
    elseif($l < 0 || $l > 20 || $c < 0 || $n < 0 || $s < 0) {
        trigger_error('Argument(s) out of range', E_USER_WARNING);
        return false;
    }
    elseif($c > $l) {
        trigger_error('Number of password capitals required exceeds password length', E_USER_WARNING);
        return false;
    }
    elseif($n > $l) {
        trigger_error('Number of password numerals exceeds password length', E_USER_WARNING);
        return false;
    }
    elseif($s > $l) {
        trigger_error('Number of password capitals exceeds password length', E_USER_WARNING);
        return false;
    }
    elseif($count > $l) {
        trigger_error('Number of password special characters exceeds specified password length', E_USER_WARNING);
        return false;
    }

    // all inputs clean, proceed to build password

    // change these strings if you want to include or exclude possible password characters
    $chars = "abcdefghijklmnopqrstuvwxyz";
    $caps = strtoupper($chars);
    $nums = "0123456789";
    $syms = "!@#$%^&*()-+?";

    // build the base password of all lower-case letters
    for($i = 0; $i < $l; $i++) {
        $out .= substr($chars, mt_rand(0, strlen($chars) - 1), 1);
    }

    // create arrays if special character(s) required
    if($count) {
        // split base password to array; create special chars array
        $tmp1 = str_split($out);
        $tmp2 = array();

        // add required special character(s) to second array
        for($i = 0; $i < $c; $i++) {
            array_push($tmp2, substr($caps, mt_rand(0, strlen($caps) - 1), 1));
        }
        for($i = 0; $i < $n; $i++) {
            array_push($tmp2, substr($nums, mt_rand(0, strlen($nums) - 1), 1));
        }
        for($i = 0; $i < $s; $i++) {
            array_push($tmp2, substr($syms, mt_rand(0, strlen($syms) - 1), 1));
        }

        // hack off a chunk of the base password array that's as big as the special chars array
        $tmp1 = array_slice($tmp1, 0, $l - $count);
        // merge special character(s) array with base password array
        $tmp1 = array_merge($tmp1, $tmp2);
        // mix the characters up
        shuffle($tmp1);
        // convert to string for output
        $out = implode('', $tmp1);
    }

    return $out;
}
?>